This invention relates to a hydrophilic material having excellent hydrophilicity and fitness to living bodies and method of manufacturing the same and, more particularly, to a hydrophilic material, which may be used as gas exchange membranes for artificial lungs, ultrafilter or permeable membranes for artificial kidney, plasma separation membranes, blood component separation membranes and porous membranes to be held in contact in use with the liquid, blood and cells of such artificial internal organs as artificial livers and artificial pancreas, external circulation treatment devices and cell cultivation devices, and method of manufacturing the same.
In the prior art, various porous membranes for gas exchange, ultrafiltration and dialysis are used for the purposes of exchanging and removing matter in the fields of medical treatment, medicines, food industries, precision engineering industries and scientific experiments.
Where a porous membrane is used in an aqueous solvent such as an aqueous solution or blood, a hydrophilic porous membrane is used, or a hydrophobic porous membrane is used after being treated to impart the hydrophilicity. As the hydrophilic porous membrane, a porous membrane of a cellulose derivative, particularly cellulose acetate, is used.
As membranes prepared by imparting hydrophilicity to a hydrophobic porous membrane, Japanese Patent Disclosures 54-153872 and 61-42304 disclose membranes prepared by immersing a hydrophobic porous membrane substrate in an organic solvent of an a alcohol, followed by water substitution, and membranes prepared covering a hydrophobic polymer membrane with a surface active agent or a hydrophilic polymer material. Further, there have been proposed a method in which a hydrophobic porous membrane substrate is covered with a hydrophilic monomer and then subjected to a bridging treatment with an electron beam or gamma rays, and a method in which a hydrophilic plastic material is coupled by optical graft-polymerization, or plasma-initiated graft-polymerization as disclosed in Japanese Patent Disclosure 62-272705, to the membrane surface.
As porous membranes fitted to living bodies, more particularly used as such medical treatment material as in contact with living body component or cells, there have been developed hydrophobic porous membranes of polyethylene and polypropylene used as artificial lungs and plasma separators, hydrophilic membranes of cellulose-based and polyvinyl alcohol-based materials and membranes of such polymer materials as polymethylmethacrylate, polyacrylonitrile and polysulfone.
However, the hydrophilic porous membrane consisting of cellulose or cellulose derivatives is subject to swelling caused by water or like solvent in use. Therefore, when this porous membrane is assembled in an apparatus, the flow path of the apparatus is liable to be blocked with the swelling of the membrane. In such a case, the performance of the membrane cannot be sufficiently obtained. Further, in the case when a hydrophilic porous membrane consisting of a cellulose-based or polyvinyl alcohol-based material is used as medical treatment membrane in contact with blood, since it has the hydroxide group in the molecule, it renders a reinforcement system strongly active. Also, it induces leukopenia. In the method, in which the surfaces of a hydrophobic porous membrane are covered with a hydrophilic material, although it is simple, it is sometimes impossible to provide permanent hydrophilicity, or the cover material is liable to be dissolved or separated.
Further considering the fitness of the medical treatment porous membrane to blood, a membrane consisting of a hydrophobic polymer material such as polyethylene and polypropylene adsorbs greater amounts of plasma protein such as fibrinogen, although the activation of the reinforcement system is slight. Also, it is reported that a membrane, the surfaces of which are hydrophilic and have high water content, and to which less plasma protein and blood cell component are attached, is subject to extreme loss of platelets when it is held in contact with blood for a long time in or outside a living body.
Further, it is reported, for instance in the Journal of Biomedical Materials Research, Vol. 20, 919-927, 1986, that block copolymers present on the substrate surface in a status that it is in separate hydrophilic and hydrophobic phases shows excellent fitness to blood. Such block copolymers may be obtained by coating the substrate surfaces with a polymer material consisting of hydrophilic and hydrophobic macromolecule chains. With this method, however, it is difficult to cover even fine and highly hydrophobic inner pore surfaces of the polypropylene porous membrane uniformly with the block copolymer. Further, the block copolymer cover layer is liable to be separated and is weak in the mechanical strength.